1. Field of the Invention
The present invention relates to printed circuit boards for use in electronic apparatus.
2. Description of the Related Art
Most electronic components used for an electronic apparatus are densely mounted on a printed circuit board and are connected to each other through wiring patterns formed on the printed circuit board.
A typical printed circuit board used for an electronic apparatus is defined by a copper-coated laminated plate including an insulating board made, for example, by dipping glass cloth formed of glass fiber in epoxy resin and by putting copper foil on the front and rear surfaces of the insulating board. An insulating board having a specified thickness of about 0.1 mm to 0.2 mm is used. The copper foil generally used is relatively inexpensive and relatively thin (18, 35, or 70 .mu.m). A printed circuit board formed by thin copper foil has a good yield due to easy copper-foil etching and is manufactured at a relatively low cost.
In a wiring pattern on a printed circuit board used for the secondary circuit of a switching power unit, for example, a large current flows when a small load resistance is connected to the output of the secondary circuit. As a result, the pattern on the printed circuit board generates resistance losses, that is copper loss, and heat is generated in the pattern. The heat generated in the pattern affects the surrounding electronic components and, for example, changes the temperature characteristics of the electronic components. When the pattern is widened to reduce copper loss, it requires a larger printed circuit board, resulting in a larger electronic apparatus.